1. Field of the Invention
The present invention relates to a method and an apparatus for reading mono-chromatic image or color image. More specifically, the invention relates to a method and an apparatus for reading mono-chromatic image or color image preventing moire from developing.
2. Description of the Prior Art
In facsimile and digital reproducing machines, a line image sensor consisting of a plurality of photoelectric converter elements are used as an image reading apparatus for reading original image. Furthermore, image reading apparatus for reading color original image use plurality of line image sensors which are comprised of a plurality of photoelectric converter elements and which have different spectral sensitivities. When a halftone dot photograph of a color-printed matter among the originals, which is usually used in an office, is read by the line image sensor, a fringe pattern (moire) that does not exist in the original image often appears in the output signals. When the original image is that of a halftone dot photograph, it is known that moire is generated when a distance among halftone dot is close to the sampling interval of the image sensor. In order to suppress the generation of moire, therefore, attempts have been made to remove halftone dot frequencies using, for example, a low-pass filter.
When the smoothing is effected by using the low pass filter, however, the edges are blurred and the resolving power decreases.